Introduction

A wide variety of age-related changes have been described in the brain of many species (1, 2 3). The aim of this study to describe the age-related histologic findings in the aged feline brain and to corroborate the usefulness of the cat as a natural animal model for the study of normal aging and neurodegenerative diseases.

Materials and methods

21 aged cats (7, 5-21 years old) and 5 young controls (6-8 months old) were used for the study. The cats were euthanised or died spontaneously suffering from a variety of disorders. The brains were routinely fixed by immersion in 4% buffered formaldehyde, embedded in paraffin wax and cut into 5μm sections. The frontal and parietal cortex were examined. Paraffin sections were stained with hematoxylin and eosin (HE), periodic acid Schiff (PAS), alkaline Congo red and Kluver-Barrera's luxol fast blue for observing general morphological changes and alkaline Congo red for viewing in polarized light amounts of amyloid. Single-labeling immunostaining by avidin-biotin peroxidase complex (ABC) method was also performed. The primary antibodies used were mouse antiserum against Aβ40, Aβ42, Aβ43, APP and rabbit antiserum against Pan β-amyloid and GFAP.

Results

Histologically, choroid plexus and meningeal fibrosis, meningeal calcification, fibrosis of the vessel walls, vascular hyalinosis and microhaemorrhages accompanied by reacting astrocytes were detected in the brains of older cats. Another finding was the presence of PAS positive foamy cells around vessels. Satellitosis and neuronophagia were found in all the brains we studied. PAS positive granular deposits affecting the pericarya and proximal dendritic tree represented lipofuscin storage. In most of the cats Lafora bodies, represented one of the 2 main PGB (polyglucosan bodies), were detected. Spheroids and neuraxonal degeneration and glial changes were obvious in most of the cases. Also, the single-labeling immunohistochemical study revealed Aβ positive material in the neuropil, the neuronal bodies and in the wall of the meningeal and parenchymal vessels.

Conclusion

All changes described in this study are similar to those seen in normal elderly humans, other primates and domestic animals or in patients suffering from neurodegenerative diseases. The above findings confirm that aged cats provide a considerable model for understanding the early changes either of normal aging or neurodegenerative diseases.

References

1. Nakamura S, et al (1996): Senile plaques in very aged cats. Acta Neuropathol 91: 437-439.

2. Papaioannou N, et al (2001): Immunohistochemical investigation of the brain of aged dogs. I. Detection of neurofibrillary tangles and 4-hydroxynonenal protein, an oxidative damage product, in senile plaques. Amyloid J Prot Fold Disord 8: 11-21.

3. Cummings BJ, et al (1996): Diffuse plaques contain C-terminal Aβ42 and not Aβ40: evidence from cats and dogs. Neurobiol Aging 17 (4): 653-659.